docs: def lines(self):
          """
          :return: list containing lines (unicode) from Dockerfile
          """
          if self.cache_content and self.cached_content:
              return self.cached_content.splitlines(True)
  
          try:
              with self._open_dockerfile('rb') as dockerfile:
                  lines = [b2u(l) for l in dockerfile.readlines()]
                  if self.cache_content:
                      self.cached_content = ''.join(lines)
                  return lines
          except (IOError, OSError) as ex:
              logger.error("Couldn't retrieve lines from dockerfile: %r", ex)
              raise